The US Open became open to professional players in 1968.
That year marked the beginning of tennis's Open Era, when professionals were permitted to compete alongside amateurs in Grand Slam tournaments. Before 1968, the U.S. National Championships were officially restricted to amateur players, even though many leading players earned money through unofficial or separate professional events.
The first Open-era US Open was played at the West Side Tennis Club in Forest Hills, New York, on outdoor grass courts. Arthur Ashe won the men's singles title, defeating Tom Okker in five sets, while Virginia Wade won the women's singles championship. The tournament offered total prize money of $100,000.
The event later moved to its current home in Flushing Meadows, Queens, in 1978 and changed from grass to clay before adopting hard courts. A common mix-up is 1970, when the US Open became the first Grand Slam to use a tiebreaker at 6–6; that was not the start of professional participation.